P0647 OBD Error Code: Problem & Solutions

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Error Code P0647 is defined as A/C Clutch Relay Control Circuit High. This code is set when the PCM detects a high voltage situation in the A/C conditioning relay control circuit. Based on the vehicle and specific malfunction, this code may be set as many as eight times before the Check Engine light is activated. When the PCM or one of the other supporting control modules has detected improper signals within the A/C clutch relay control electrical circuit, code P0647 will be set.

The P0647 code is a generic OBD-II trouble code that detects a problem with the A/C (air conditioning) clutch relay control circuit. The job of the A/C (air-conditioning) clutch relay control circuit is to control the air conditioning’s operation. This code means that the A/C clutch relay control circuit is malfunctioning due to a faulty control relay, compressor driver, damaged wiring components. A/C clutch relay circuit is monitored when ignition is on and battery voltage is greater than 10.4 volts. Code P0647 is set by the PCM when it detects a too high voltage condition within the air conditioning relay control circuit.

What causes this problem with the A/C Clutch Relay Control Circuit High?

• Open or shorted A/C Clutch Relay Harness
• Defective A/C Clutch Relay
• Poor electrical connection
• Faulty Control Module
• Loose or broken ground strap
• Blown Fuses
• Flawed A/C Compressor
• Faulty PCM

1. A/C Clutch Relay - Almost every single electrical system on a car is powered through some kind of switch or electrical relay, and the AC system and compressor are no exception. The AC compressor relay is responsible for supplying power to the AC compressor and clutch. Replace or repair it if you discover it faulty.
2. A/C Compressor Clutch - It is a belt drive attached to the engine spins constantly, providing energy for the AC compressor. The belt turns a rotor, which has a friction plate attached to it. Near the rotor is an electromagnet--a coil of wire which produces a magnetic field when current is run through it. It should be inspected thoroughly and repaired as required.
3. A/C Compressor - An air conditioner compressor is the component in the system that raises the temperature and pressure of the vapor refrigerant that leaves the evaporator coil. Check it out thoroughly and if you find it faulty replace it.

This issue should not be unattended as it could develop into something much more serious fairly quickly. Below are the common symptoms for the code P0647. If you experience these please bring your vehicle to a reputable repair facility.

• A/C may not work well
• A/C may not work at all
• Illuminated check engine light

Due to trouble code P0647 you may not face any drivability issues; however, it is possible that the air conditioning system will not properly work. Following repairs and replacements may help you to fix this code:

• Replacement of the A/C clutch relay
• Repair or replacement of faulty wiring
• Repair or replacement of ground straps
• Replacement of control module
• Replacement of the blown fuse or fuse-able link (if applicable)
• Evacuate and recharging of the A/C system
• Cleaning connectors corrosion
• Replacement of the A/C clutch
• Replacement of the A/C compressor
• Replacement or re-flashing of PCM

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To correct or fix this code one should seek assistance from a trained automotive diagnostician but if you want to do it by yourself, please follow the below mentioned steps:

• Begin with a visual inspection of all wiring and connectors.
• Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary.
• Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data.
• This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored.
• Continue by clearing the code and operating the vehicle to see if it returns.
• This will help to determine whether or not the malfunction is intermittent.
• After the codes are cleared, test drives the vehicle to see if the code returns.
• If the code fails to immediately return, you may have an intermittent condition.
• A specialized diagnostic CAN scanner will show pin values and control module operation without risking a meltdown.
• It can accurately diagnose computer and circuitry problems by monitoring vehicle operation while the vehicle is being operated.
• To diagnose this type of code using a digital volt ohmmeter would entail probing thousands of circuits, independently.
• Control module ground circuits should be tested for continuity with battery ground.
• These types of codes are frequently caused by defective or disconnected system grounds.
• Look for loose or corroded electrical connectors that may increase circuit resistance and cause these types of codes to be stored. Obtain a CAN bus system wiring diagram and/or pin out value chart, and then use the digital volt ohmmeter to test continuity between individual controller connectors.
• Compare your findings with the manufacturer’s referenced values and repair open or shorted circuits as required.

Common Mistakes When Diagnosing the P0647 Code

Symptoms and stored codes that are present as a reaction to a communication failure are often misdiagnosed and repaired as the cause of the problem. Obviously, this leads to an unsuccessful repair.